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 $126.38   3.584%   $130.9095   $130.91   $130.90   $130.90  
  Purchase #2 $249.51   11.308%   $277.7246   $277.72   $277.70   $277.70  
  Purchase #3 $85.78   13.283%   $97.1742   $97.17   $97.15   $97.20  
  Purchase #4 $229.67   12.187%   $257.6599   $257.66   $257.65   $257.70  
  Purchase #5 $48.66   10.646%   $53.8403   $53.84   $53.85   $53.80  
  Purchase #6 $189.51   3.284%   $195.7335   $195.73   $195.75   $195.70  
  Purchase #7 $17.93   7.515%   $19.2774   $19.28   $19.30   $19.30  
  7 purchase totals = $947.44       $1,032.3194   $1,032.31   $1,032.30   $1,032.30