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 $124.91   10.460%   $137.9756   $137.98   $138.00   $138.00  
  Purchase #2 $201.79   7.355%   $216.6317   $216.63   $216.65   $216.60  
  Purchase #3 $73.97   6.478%   $78.7618   $78.76   $78.75   $78.80  
  Purchase #4 $141.45   7.229%   $151.6754   $151.68   $151.70   $151.70  
  Purchase #5 $239.68   13.643%   $272.3795   $272.38   $272.40   $272.40  
  Purchase #6 $247.66   8.779%   $269.4021   $269.40   $269.40   $269.40  
  Purchase #7 $60.52   9.567%   $66.3099   $66.31   $66.30   $66.30  
  7 purchase totals = $1,089.98       $1,193.1360   $1,193.14   $1,193.20   $1,193.20