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 $111.98   6.166%   $118.8847   $118.88   $118.90   $118.90  
  Purchase #2 $200.90   13.524%   $228.0697   $228.07   $228.05   $228.10  
  Purchase #3 $23.40   6.654%   $24.957   $24.96   $24.95   $25.00  
  Purchase #4 $174.82   7.276%   $187.5399   $187.54   $187.55   $187.50  
  Purchase #5 $60.59   7.269%   $64.9943   $64.99   $65.00   $65.00  
  Purchase #6 $236.78   11.223%   $263.3538   $263.35   $263.35   $263.40  
  Purchase #7 $59.80   5.127%   $62.8659   $62.87   $62.85   $62.90  
  7 purchase totals = $868.27       $950.6653   $950.66   $950.65   $950.80