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 $29.65   13.269%   $33.5843   $33.58   $33.60   $33.60  
  Purchase #2 $123.33   10.820%   $136.6743   $136.67   $136.65   $136.70  
  Purchase #3 $214.95   6.775%   $229.5129   $229.51   $229.50   $229.50  
  Purchase #4 $225.54   12.853%   $254.5287   $254.53   $254.55   $254.50  
  Purchase #5 $8.48   11.169%   $9.4271   $9.43   $9.45   $9.40  
  Purchase #6 $208.48   5.152%   $219.2209   $219.22   $219.20   $219.20  
  Purchase #7 $136.84   10.717%   $151.5051   $151.51   $151.50   $151.50  
  7 purchase totals = $947.27       $1,034.4533   $1,034.45   $1,034.45   $1,034.40