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 $88.97   6.796%   $95.0164   $95.02   $95.00   $95.00  
  Purchase #2 $79.55   9.408%   $87.0341   $87.03   $87.05   $87.00  
  Purchase #3 $236.37   11.594%   $263.7747   $263.77   $263.75   $263.80  
  Purchase #4 $173.67   8.666%   $188.7202   $188.72   $188.70   $188.70  
  Purchase #5 $238.40   12.146%   $267.3561   $267.36   $267.35   $267.40  
  Purchase #6 $45.93   11.626%   $51.2698   $51.27   $51.25   $51.30  
  Purchase #7 $25.65   4.729%   $26.863   $26.86   $26.85   $26.90  
  7 purchase totals = $888.54       $980.0343   $980.03   $979.95   $980.10