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 $217.97   11.164%   $242.3042   $242.30   $242.30   $242.30  
  Purchase #2 $186.55   3.347%   $192.7938   $192.79   $192.80   $192.80  
  Purchase #3 $85.86   9.476%   $93.9961   $94.00   $94.00   $94.00  
  Purchase #4 $135.50   12.198%   $152.0283   $152.03   $152.05   $152.00  
  Purchase #5 $175.41   10.319%   $193.5106   $193.51   $193.50   $193.50  
  Purchase #6 $118.76   9.112%   $129.5814   $129.58   $129.60   $129.60  
  Purchase #7 $240.84   12.607%   $271.2027   $271.20   $271.20   $271.20  
  7 purchase totals = $1,160.89       $1,275.4171   $1,275.41   $1,275.45   $1,275.40