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 $143.77   6.232%   $152.7297   $152.73   $152.75   $152.70  
  Purchase #2 $215.38   5.604%   $227.4499   $227.45   $227.45   $227.40  
  Purchase #3 $172.93   5.608%   $182.6279   $182.63   $182.65   $182.60  
  Purchase #4 $191.43   6.667%   $204.1926   $204.19   $204.20   $204.20  
  Purchase #5 $88.48   11.823%   $98.941   $98.94   $98.95   $98.90  
  Purchase #6 $105.93   12.208%   $118.8619   $118.86   $118.85   $118.90  
  Purchase #7 $39.34   13.148%   $44.5124   $44.51   $44.50   $44.50  
  7 purchase totals = $957.26       $1,029.3154   $1,029.31   $1,029.35   $1,029.20