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 $201.26   10.842%   $223.0806   $223.08   $223.10   $223.10  
  Purchase #2 $205.39   4.623%   $214.8852   $214.89   $214.90   $214.90  
  Purchase #3 $31.76   3.739%   $32.9475   $32.95   $32.95   $32.90  
  Purchase #4 $173.78   12.494%   $195.4921   $195.49   $195.50   $195.50  
  Purchase #5 $120.35   9.115%   $131.3199   $131.32   $131.30   $131.30  
  Purchase #6 $102.65   5.396%   $108.189   $108.19   $108.20   $108.20  
  Purchase #7 $48.86   3.748%   $50.6913   $50.69   $50.70   $50.70  
  7 purchase totals = $884.05       $956.6056   $956.61   $956.65   $956.60