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 $146.98   6.258%   $156.178   $156.18   $156.20   $156.20  
  Purchase #2 $54.40   11.368%   $60.5842   $60.58   $60.60   $60.60  
  Purchase #3 $118.73   11.627%   $132.5347   $132.53   $132.55   $132.50  
  Purchase #4 $206.63   6.770%   $220.6189   $220.62   $220.60   $220.60  
  Purchase #5 $180.68   12.636%   $203.5107   $203.51   $203.50   $203.50  
  Purchase #6 $234.38   8.780%   $254.9586   $254.96   $254.95   $255.00  
  Purchase #7 $210.93   13.449%   $239.298   $239.30   $239.30   $239.30  
  7 purchase totals = $1,152.73       $1,267.6831   $1,267.68   $1,267.70   $1,267.70