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 $226.74   8.829%   $246.7589   $246.76   $246.75   $246.80  
  Purchase #2 $93.43   6.688%   $99.6786   $99.68   $99.70   $99.70  
  Purchase #3 $74.98   11.651%   $83.7159   $83.72   $83.70   $83.70  
  Purchase #4 $94.84   3.233%   $97.9062   $97.91   $97.90   $97.90  
  Purchase #5 $127.98   12.494%   $143.9698   $143.97   $143.95   $144.00  
  Purchase #6 $160.49   6.168%   $170.389   $170.39   $170.40   $170.40  
  Purchase #7 $210.73   9.376%   $230.488   $230.49   $230.50   $230.50  
  7 purchase totals = $989.19       $1,072.9064   $1,072.92   $1,072.90   $1,073.00