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 $188.29   12.272%   $211.3969   $211.40   $211.40   $211.40  
  Purchase #2 $68.28   13.275%   $77.3442   $77.34   $77.35   $77.30  
  Purchase #3 $49.31   4.558%   $51.5575   $51.56   $51.55   $51.60  
  Purchase #4 $126.38   13.738%   $143.7421   $143.74   $143.75   $143.70  
  Purchase #5 $242.84   13.523%   $275.6793   $275.68   $275.70   $275.70  
  Purchase #6 $191.61   8.189%   $207.3009   $207.30   $207.30   $207.30  
  Purchase #7 $77.40   4.629%   $80.9828   $80.98   $81.00   $81.00  
  7 purchase totals = $944.11       $1,048.0037   $1,048.00   $1,048.05   $1,048.00