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 $168.26   13.516%   $191.002   $191.00   $191.00   $191.00  
  Purchase #2 $23.52   6.309%   $25.0039   $25.00   $25.00   $25.00  
  Purchase #3 $28.87   7.460%   $31.0237   $31.02   $31.00   $31.00  
  Purchase #4 $141.88   12.659%   $159.8406   $159.84   $159.85   $159.80  
  Purchase #5 $64.89   4.107%   $67.555   $67.56   $67.55   $67.60  
  Purchase #6 $68.27   11.554%   $76.1579   $76.16   $76.15   $76.20  
  Purchase #7 $96.68   9.660%   $106.0193   $106.02   $106.00   $106.00  
  7 purchase totals = $592.37       $656.6024   $656.60   $656.55   $656.60