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 $206.38   12.623%   $232.4313   $232.43   $232.45   $232.40  
  Purchase #2 $95.81   7.175%   $102.6844   $102.68   $102.70   $102.70  
  Purchase #3 $129.34   7.229%   $138.69   $138.69   $138.70   $138.70  
  Purchase #4 $113.25   13.580%   $128.6294   $128.63   $128.65   $128.60  
  Purchase #5 $198.84   6.825%   $212.4108   $212.41   $212.40   $212.40  
  Purchase #6 $171.58   5.228%   $180.5502   $180.55   $180.55   $180.60  
  Purchase #7 $18.62   6.266%   $19.7867   $19.79   $19.80   $19.80  
  7 purchase totals = $933.82       $1,015.1828   $1,015.18   $1,015.25   $1,015.20