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 $51.92   8.337%   $56.2486   $56.25   $56.25   $56.20  
  Purchase #2 $226.97   5.144%   $238.6453   $238.65   $238.65   $238.60  
  Purchase #3 $123.37   10.424%   $136.2301   $136.23   $136.25   $136.20  
  Purchase #4 $41.49   8.146%   $44.8698   $44.87   $44.85   $44.90  
  Purchase #5 $232.61   3.362%   $240.4303   $240.43   $240.45   $240.40  
  Purchase #6 $169.26   12.431%   $190.3007   $190.30   $190.30   $190.30  
  Purchase #7 $217.50   5.337%   $229.108   $229.11   $229.10   $229.10  
  7 purchase totals = $1,063.12       $1,135.8328   $1,135.84   $1,135.85   $1,135.70