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 $189.83   8.368%   $205.715   $205.72   $205.70   $205.70  
  Purchase #2 $234.48   4.433%   $244.8745   $244.87   $244.85   $244.90  
  Purchase #3 $61.53   11.528%   $68.6232   $68.62   $68.60   $68.60  
  Purchase #4 $135.65   4.160%   $141.293   $141.29   $141.30   $141.30  
  Purchase #5 $144.56   5.344%   $152.2853   $152.29   $152.30   $152.30  
  Purchase #6 $25.49   7.437%   $27.3857   $27.39   $27.40   $27.40  
  Purchase #7 $80.61   7.585%   $86.7243   $86.72   $86.70   $86.70  
  7 purchase totals = $872.15       $926.9010   $926.90   $926.85   $926.90