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 $189.33   13.272%   $214.4579   $214.46   $214.45   $214.50  
  Purchase #2 $33.65   3.714%   $34.8998   $34.90   $34.90   $34.90  
  Purchase #3 $220.58   6.812%   $235.6059   $235.61   $235.60   $235.60  
  Purchase #4 $54.54   10.690%   $60.3703   $60.37   $60.35   $60.40  
  Purchase #5 $244.30   5.849%   $258.5891   $258.59   $258.60   $258.60  
  Purchase #6 $165.90   9.707%   $182.0039   $182.00   $182.00   $182.00  
  Purchase #7 $64.96   5.515%   $68.5425   $68.54   $68.55   $68.50  
  7 purchase totals = $973.26       $1,054.4694   $1,054.47   $1,054.45   $1,054.50