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 $92.66   9.221%   $101.2042   $101.20   $101.20   $101.20  
  Purchase #2 $223.32   6.815%   $238.5393   $238.54   $238.55   $238.50  
  Purchase #3 $101.77   9.687%   $111.6285   $111.63   $111.65   $111.60  
  Purchase #4 $142.69   8.343%   $154.5946   $154.59   $154.60   $154.60  
  Purchase #5 $71.89   10.148%   $79.1854   $79.19   $79.20   $79.20  
  Purchase #6 $219.89   4.716%   $230.26   $230.26   $230.25   $230.30  
  Purchase #7 $244.77   12.751%   $275.9806   $275.98   $276.00   $276.00  
  7 purchase totals = $1,096.99       $1,191.3926   $1,191.39   $1,191.45   $1,191.40