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 $137.96   11.368%   $153.6433   $153.64   $153.65   $153.60  
  Purchase #2 $173.43   12.456%   $195.0324   $195.03   $195.05   $195.00  
  Purchase #3 $188.98   7.704%   $203.539   $203.54   $203.55   $203.50  
  Purchase #4 $55.98   12.795%   $63.1426   $63.14   $63.15   $63.10  
  Purchase #5 $119.89   4.850%   $125.7047   $125.70   $125.70   $125.70  
  Purchase #6 $125.38   10.328%   $138.3292   $138.33   $138.35   $138.30  
  Purchase #7 $160.93   8.853%   $175.1771   $175.18   $175.20   $175.20  
  7 purchase totals = $962.55       $1,054.5683   $1,054.56   $1,054.65   $1,054.40