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 $97.43   7.434%   $104.6729   $104.67   $104.65   $104.70  
  Purchase #2 $33.65   11.255%   $37.4373   $37.44   $37.45   $37.40  
  Purchase #3 $27.33   8.144%   $29.5558   $29.56   $29.55   $29.60  
  Purchase #4 $59.94   5.225%   $63.0719   $63.07   $63.05   $63.10  
  Purchase #5 $246.74   10.515%   $272.6847   $272.68   $272.70   $272.70  
  Purchase #6 $201.42   3.190%   $207.8453   $207.85   $207.85   $207.80  
  Purchase #7 $56.63   6.451%   $60.2832   $60.28   $60.30   $60.30  
  7 purchase totals = $723.14       $775.5511   $775.55   $775.55   $775.60