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 $84.52   3.227%   $87.2475   $87.25   $87.25   $87.20  
  Purchase #2 $84.96   4.680%   $88.9361   $88.94   $88.95   $88.90  
  Purchase #3 $69.74   5.171%   $73.3463   $73.35   $73.35   $73.30  
  Purchase #4 $31.27   11.190%   $34.7691   $34.77   $34.75   $34.80  
  Purchase #5 $186.74   3.532%   $193.3357   $193.34   $193.35   $193.30  
  Purchase #6 $201.96   3.516%   $209.0609   $209.06   $209.05   $209.10  
  Purchase #7 $110.74   6.578%   $118.0245   $118.02   $118.00   $118.00  
  7 purchase totals = $769.93       $804.7201   $804.73   $804.70   $804.60