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 $70.60   9.812%   $77.5273   $77.53   $77.55   $77.50  
  Purchase #2 $245.55   8.352%   $266.0583   $266.06   $266.05   $266.10  
  Purchase #3 $43.95   3.746%   $45.5964   $45.60   $45.60   $45.60  
  Purchase #4 $161.67   8.432%   $175.302   $175.30   $175.30   $175.30  
  Purchase #5 $26.96   8.681%   $29.3004   $29.30   $29.30   $29.30  
  Purchase #6 $235.98   10.402%   $260.5266   $260.53   $260.55   $260.50  
  Purchase #7 $153.65   13.431%   $174.2867   $174.29   $174.30   $174.30  
  7 purchase totals = $938.36       $1,028.5977   $1,028.61   $1,028.65   $1,028.60