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 $52.95   11.303%   $58.9349   $58.93   $58.95   $58.90  
  Purchase #2 $95.84   12.398%   $107.7222   $107.72   $107.70   $107.70  
  Purchase #3 $155.79   11.236%   $173.2946   $173.29   $173.30   $173.30  
  Purchase #4 $139.74   5.562%   $147.5123   $147.51   $147.50   $147.50  
  Purchase #5 $89.51   6.234%   $95.0901   $95.09   $95.10   $95.10  
  Purchase #6 $146.70   10.478%   $162.0712   $162.07   $162.05   $162.10  
  Purchase #7 $227.45   13.772%   $258.7744   $258.77   $258.75   $258.80  
  7 purchase totals = $907.98       $1,003.3997   $1,003.38   $1,003.35   $1,003.40