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 $58.29   3.839%   $60.5278   $60.53   $60.55   $60.50  
  Purchase #2 $119.55   12.115%   $134.0335   $134.03   $134.05   $134.00  
  Purchase #3 $183.56   7.375%   $197.0976   $197.10   $197.10   $197.10  
  Purchase #4 $120.53   12.515%   $135.6143   $135.61   $135.60   $135.60  
  Purchase #5 $117.94   11.608%   $131.6305   $131.63   $131.65   $131.60  
  Purchase #6 $60.58   3.725%   $62.8366   $62.84   $62.85   $62.80  
  Purchase #7 $206.95   11.772%   $231.3122   $231.31   $231.30   $231.30  
  7 purchase totals = $867.40       $953.0525   $953.05   $953.10   $952.90