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 $56.27   12.192%   $63.1304   $63.13   $63.15   $63.10  
  Purchase #2 $91.72   4.717%   $96.0464   $96.05   $96.05   $96.00  
  Purchase #3 $87.51   8.747%   $95.1645   $95.16   $95.15   $95.20  
  Purchase #4 $138.61   7.811%   $149.4368   $149.44   $149.45   $149.40  
  Purchase #5 $235.84   4.872%   $247.3301   $247.33   $247.35   $247.30  
  Purchase #6 $174.33   6.663%   $185.9456   $185.95   $185.95   $185.90  
  Purchase #7 $152.63   10.230%   $168.244   $168.24   $168.25   $168.20  
  7 purchase totals = $936.91       $1,005.2978   $1,005.30   $1,005.35   $1,005.10