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 $233.27   5.251%   $245.519   $245.52   $245.50   $245.50  
  Purchase #2 $25.79   5.278%   $27.1512   $27.15   $27.15   $27.20  
  Purchase #3 $237.38   11.506%   $264.6929   $264.69   $264.70   $264.70  
  Purchase #4 $131.84   4.700%   $138.0365   $138.04   $138.05   $138.00  
  Purchase #5 $40.29   4.625%   $42.1534   $42.15   $42.15   $42.20  
  Purchase #6 $183.99   5.741%   $194.5529   $194.55   $194.55   $194.60  
  Purchase #7 $128.50   6.474%   $136.8191   $136.82   $136.80   $136.80  
  7 purchase totals = $981.06       $1,048.9250   $1,048.92   $1,048.90   $1,049.00