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 $106.42   12.237%   $119.4426   $119.44   $119.45   $119.40  
  Purchase #2 $196.84   13.700%   $223.8071   $223.81   $223.80   $223.80  
  Purchase #3 $32.37   13.486%   $36.7354   $36.74   $36.75   $36.70  
  Purchase #4 $206.90   12.234%   $232.2121   $232.21   $232.20   $232.20  
  Purchase #5 $238.32   6.604%   $254.0587   $254.06   $254.05   $254.10  
  Purchase #6 $58.26   12.661%   $65.6363   $65.64   $65.65   $65.60  
  Purchase #7 $200.94   9.193%   $219.4124   $219.41   $219.40   $219.40  
  7 purchase totals = $1,040.05       $1,151.3046   $1,151.31   $1,151.30   $1,151.20