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 $202.89   5.246%   $213.5336   $213.53   $213.55   $213.50  
  Purchase #2 $50.27   9.616%   $55.104   $55.10   $55.10   $55.10  
  Purchase #3 $235.48   3.827%   $244.4918   $244.49   $244.50   $244.50  
  Purchase #4 $90.63   6.756%   $96.753   $96.75   $96.75   $96.80  
  Purchase #5 $218.96   4.165%   $228.0797   $228.08   $228.10   $228.10  
  Purchase #6 $210.30   9.703%   $230.7054   $230.71   $230.70   $230.70  
  Purchase #7 $44.65   8.825%   $48.5904   $48.59   $48.60   $48.60  
  7 purchase totals = $1,053.18       $1,117.2579   $1,117.25   $1,117.30   $1,117.30