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 $73.45   13.841%   $83.6162   $83.62   $83.60   $83.60  
  Purchase #2 $199.86   5.550%   $210.9522   $210.95   $210.95   $211.00  
  Purchase #3 $173.40   12.717%   $195.4513   $195.45   $195.45   $195.50  
  Purchase #4 $236.43   13.309%   $267.8965   $267.90   $267.90   $267.90  
  Purchase #5 $155.57   10.162%   $171.379   $171.38   $171.40   $171.40  
  Purchase #6 $87.57   5.656%   $92.523   $92.52   $92.50   $92.50  
  Purchase #7 $158.30   11.650%   $176.742   $176.74   $176.75   $176.70  
  7 purchase totals = $1,084.58       $1,198.5602   $1,198.56   $1,198.55   $1,198.60