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 $70.58   6.206%   $74.9602   $74.96   $74.95   $75.00  
  Purchase #2 $172.34   11.573%   $192.2849   $192.28   $192.30   $192.30  
  Purchase #3 $94.90   6.648%   $101.209   $101.21   $101.20   $101.20  
  Purchase #4 $234.46   8.636%   $254.708   $254.71   $254.70   $254.70  
  Purchase #5 $96.40   5.388%   $101.594   $101.59   $101.60   $101.60  
  Purchase #6 $177.36   13.792%   $201.8215   $201.82   $201.80   $201.80  
  Purchase #7 $98.68   10.118%   $108.6644   $108.66   $108.65   $108.70  
  7 purchase totals = $944.72       $1,035.2420   $1,035.23   $1,035.20   $1,035.30