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 $235.49   8.506%   $255.5208   $255.52   $255.50   $255.50  
  Purchase #2 $152.65   10.629%   $168.8752   $168.88   $168.90   $168.90  
  Purchase #3 $36.59   12.621%   $41.208   $41.21   $41.20   $41.20  
  Purchase #4 $232.86   6.403%   $247.77   $247.77   $247.75   $247.80  
  Purchase #5 $8.64   5.809%   $9.1419   $9.14   $9.15   $9.10  
  Purchase #6 $242.79   10.490%   $268.2587   $268.26   $268.25   $268.30  
  Purchase #7 $54.51   12.787%   $61.4802   $61.48   $61.50   $61.50  
  7 purchase totals = $963.53       $1,052.2548   $1,052.26   $1,052.25   $1,052.30