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 $60.41   12.826%   $68.1582   $68.16   $68.15   $68.20  
  Purchase #2 $172.51   12.254%   $193.6494   $193.65   $193.65   $193.60  
  Purchase #3 $106.66   3.461%   $110.3515   $110.35   $110.35   $110.40  
  Purchase #4 $68.55   12.400%   $77.0502   $77.05   $77.05   $77.10  
  Purchase #5 $151.58   5.163%   $159.4061   $159.41   $159.40   $159.40  
  Purchase #6 $194.76   3.102%   $200.8015   $200.80   $200.80   $200.80  
  Purchase #7 $152.81   3.828%   $158.6596   $158.66   $158.65   $158.70  
  7 purchase totals = $907.28       $968.0765   $968.08   $968.05   $968.20