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 $234.59   9.439%   $256.733   $256.73   $256.75   $256.70  
  Purchase #2 $205.57   11.381%   $228.9659   $228.97   $228.95   $229.00  
  Purchase #3 $14.62   12.829%   $16.4956   $16.50   $16.50   $16.50  
  Purchase #4 $52.61   5.446%   $55.4751   $55.48   $55.50   $55.50  
  Purchase #5 $238.49   8.770%   $259.4056   $259.41   $259.40   $259.40  
  Purchase #6 $160.79   9.646%   $176.2998   $176.30   $176.30   $176.30  
  Purchase #7 $228.77   6.303%   $243.1894   $243.19   $243.20   $243.20  
  7 purchase totals = $1,135.44       $1,236.5644   $1,236.58   $1,236.60   $1,236.60