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 $62.98   8.860%   $68.56   $68.56   $68.55   $68.60  
  Purchase #2 $81.65   8.502%   $88.5919   $88.59   $88.60   $88.60  
  Purchase #3 $36.97   6.402%   $39.3368   $39.34   $39.35   $39.30  
  Purchase #4 $152.31   8.329%   $164.9959   $165.00   $165.00   $165.00  
  Purchase #5 $128.74   5.203%   $135.4383   $135.44   $135.45   $135.40  
  Purchase #6 $215.99   13.532%   $245.2178   $245.22   $245.20   $245.20  
  Purchase #7 $246.49   7.590%   $265.1986   $265.20   $265.20   $265.20  
  7 purchase totals = $925.13       $1,007.3393   $1,007.35   $1,007.35   $1,007.30