Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $184.80   3.862%   $191.937   $191.94   $191.95   $191.90  
  Purchase #2 $101.74   11.769%   $113.7138   $113.71   $113.70   $113.70  
  Purchase #3 $192.66   7.781%   $207.6509   $207.65   $207.65   $207.70  
  Purchase #4 $228.62   12.639%   $257.5153   $257.52   $257.50   $257.50  
  Purchase #5 $212.67   6.403%   $226.2873   $226.29   $226.30   $226.30  
  Purchase #6 $207.65   11.295%   $231.1041   $231.10   $231.10   $231.10  
  Purchase #7 $209.70   7.464%   $225.352   $225.35   $225.35   $225.40  
  7 purchase totals = $1,337.84       $1,453.5604   $1,453.56   $1,453.55   $1,453.60