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 $145.77   4.251%   $151.9667   $151.97   $151.95   $152.00  
  Purchase #2 $245.86   12.319%   $276.1475   $276.15   $276.15   $276.10  
  Purchase #3 $70.76   9.277%   $77.3244   $77.32   $77.30   $77.30  
  Purchase #4 $46.69   8.272%   $50.5522   $50.55   $50.55   $50.60  
  Purchase #5 $178.93   8.250%   $193.6917   $193.69   $193.70   $193.70  
  Purchase #6 $169.62   6.444%   $180.5503   $180.55   $180.55   $180.60  
  Purchase #7 $64.77   13.124%   $73.2704   $73.27   $73.25   $73.30  
  7 purchase totals = $922.40       $1,003.5032   $1,003.50   $1,003.45   $1,003.60