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 $145.36   3.515%   $150.4694   $150.47   $150.45   $150.50  
  Purchase #2 $198.78   13.684%   $225.9811   $225.98   $226.00   $226.00  
  Purchase #3 $13.34   4.345%   $13.9196   $13.92   $13.90   $13.90  
  Purchase #4 $119.30   9.711%   $130.8852   $130.89   $130.90   $130.90  
  Purchase #5 $204.62   5.674%   $216.2301   $216.23   $216.25   $216.20  
  Purchase #6 $106.29   13.399%   $120.5318   $120.53   $120.55   $120.50  
  Purchase #7 $164.42   10.544%   $181.7564   $181.76   $181.75   $181.80  
  7 purchase totals = $952.11       $1,039.7736   $1,039.78   $1,039.80   $1,039.80