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 $44.62   3.731%   $46.2848   $46.28   $46.30   $46.30  
  Purchase #2 $187.87   10.332%   $207.2807   $207.28   $207.30   $207.30  
  Purchase #3 $25.59   10.835%   $28.3627   $28.36   $28.35   $28.40  
  Purchase #4 $207.67   6.245%   $220.639   $220.64   $220.65   $220.60  
  Purchase #5 $185.43   9.168%   $202.4302   $202.43   $202.45   $202.40  
  Purchase #6 $9.47   5.244%   $9.9666   $9.97   $9.95   $10.00  
  Purchase #7 $91.79   5.220%   $96.5814   $96.58   $96.60   $96.60  
  7 purchase totals = $752.44       $811.5454   $811.54   $811.60   $811.60