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 $58.87   9.739%   $64.6033   $64.60   $64.60   $64.60  
  Purchase #2 $124.99   12.108%   $140.1238   $140.12   $140.10   $140.10  
  Purchase #3 $48.29   8.118%   $52.2102   $52.21   $52.20   $52.20  
  Purchase #4 $224.54   5.444%   $236.764   $236.76   $236.75   $236.80  
  Purchase #5 $186.37   10.199%   $205.3779   $205.38   $205.40   $205.40  
  Purchase #6 $115.65   11.241%   $128.6502   $128.65   $128.65   $128.70  
  Purchase #7 $8.71   3.294%   $8.9969   $9.00   $9.00   $9.00  
  7 purchase totals = $767.42       $836.7263   $836.72   $836.70   $836.80