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 $236.96   13.394%   $268.6984   $268.70   $268.70   $268.70  
  Purchase #2 $34.70   11.118%   $38.5579   $38.56   $38.55   $38.60  
  Purchase #3 $8.83   5.566%   $9.3215   $9.32   $9.30   $9.30  
  Purchase #4 $45.85   13.701%   $52.1319   $52.13   $52.15   $52.10  
  Purchase #5 $56.90   4.756%   $59.6062   $59.61   $59.60   $59.60  
  Purchase #6 $118.79   9.817%   $130.4516   $130.45   $130.45   $130.50  
  Purchase #7 $203.97   6.869%   $217.9807   $217.98   $218.00   $218.00  
  7 purchase totals = $706.00       $776.7482   $776.75   $776.75   $776.80