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 $62.46   6.218%   $66.3438   $66.34   $66.35   $66.30  
  Purchase #2 $97.41   11.249%   $108.3677   $108.37   $108.35   $108.40  
  Purchase #3 $171.93   5.706%   $181.7403   $181.74   $181.75   $181.70  
  Purchase #4 $95.82   9.333%   $104.7629   $104.76   $104.75   $104.80  
  Purchase #5 $241.56   5.379%   $254.5535   $254.55   $254.55   $254.60  
  Purchase #6 $117.88   5.580%   $124.4577   $124.46   $124.45   $124.50  
  Purchase #7 $87.65   3.799%   $90.9798   $90.98   $91.00   $91.00  
  7 purchase totals = $874.71       $931.2057   $931.20   $931.20   $931.30