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 $88.35   7.331%   $94.8269   $94.83   $94.85   $94.80  
  Purchase #2 $47.58   4.118%   $49.5393   $49.54   $49.55   $49.50  
  Purchase #3 $47.45   9.453%   $51.9354   $51.94   $51.95   $51.90  
  Purchase #4 $91.68   12.321%   $102.9759   $102.98   $103.00   $103.00  
  Purchase #5 $233.34   11.248%   $259.5861   $259.59   $259.60   $259.60  
  Purchase #6 $189.52   13.867%   $215.8007   $215.80   $215.80   $215.80  
  Purchase #7 $144.77   6.319%   $153.918   $153.92   $153.90   $153.90  
  7 purchase totals = $842.69       $928.5823   $928.60   $928.65   $928.50