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 $165.78   4.268%   $172.8555   $172.86   $172.85   $172.90  
  Purchase #2 $220.64   12.191%   $247.5382   $247.54   $247.55   $247.50  
  Purchase #3 $99.93   8.427%   $108.3511   $108.35   $108.35   $108.40  
  Purchase #4 $194.79   12.620%   $219.3725   $219.37   $219.35   $219.40  
  Purchase #5 $100.43   4.207%   $104.6551   $104.66   $104.65   $104.70  
  Purchase #6 $102.90   5.232%   $108.2837   $108.28   $108.30   $108.30  
  Purchase #7 $143.52   11.350%   $159.8095   $159.81   $159.80   $159.80  
  7 purchase totals = $1,027.99       $1,120.8656   $1,120.87   $1,120.85   $1,121.00