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 $14.98   11.744%   $16.7393   $16.74   $16.75   $16.70  
  Purchase #2 $219.56   7.299%   $235.5857   $235.59   $235.60   $235.60  
  Purchase #3 $61.88   10.536%   $68.3997   $68.40   $68.40   $68.40  
  Purchase #4 $81.90   11.574%   $91.3791   $91.38   $91.40   $91.40  
  Purchase #5 $222.66   6.447%   $237.0149   $237.01   $237.00   $237.00  
  Purchase #6 $192.40   9.301%   $210.2951   $210.30   $210.30   $210.30  
  Purchase #7 $162.26   9.112%   $177.0451   $177.05   $177.05   $177.00  
  7 purchase totals = $955.64       $1,036.4589   $1,036.47   $1,036.50   $1,036.40