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 $46.89   6.733%   $50.0471   $50.05   $50.05   $50.00  
  Purchase #2 $112.51   11.179%   $125.0875   $125.09   $125.10   $125.10  
  Purchase #3 $20.73   8.373%   $22.4657   $22.47   $22.45   $22.50  
  Purchase #4 $183.35   13.201%   $207.554   $207.55   $207.55   $207.60  
  Purchase #5 $134.46   12.266%   $150.9529   $150.95   $150.95   $151.00  
  Purchase #6 $249.47   13.681%   $283.6   $283.60   $283.60   $283.60  
  Purchase #7 $206.52   6.230%   $219.3862   $219.39   $219.40   $219.40  
  7 purchase totals = $953.93       $1,059.0934   $1,059.10   $1,059.10   $1,059.20