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 $192.64   5.249%   $202.7517   $202.75   $202.75   $202.80  
  Purchase #2 $131.34   3.282%   $135.6506   $135.65   $135.65   $135.70  
  Purchase #3 $24.34   9.229%   $26.5863   $26.59   $26.60   $26.60  
  Purchase #4 $167.49   8.428%   $181.6061   $181.61   $181.60   $181.60  
  Purchase #5 $27.41   9.179%   $29.926   $29.93   $29.95   $29.90  
  Purchase #6 $97.34   4.827%   $102.0386   $102.04   $102.05   $102.00  
  Purchase #7 $209.84   3.169%   $216.4898   $216.49   $216.50   $216.50  
  7 purchase totals = $850.40       $895.0491   $895.06   $895.10   $895.10