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 $108.51   10.159%   $119.5335   $119.53   $119.55   $119.50  
  Purchase #2 $222.78   11.141%   $247.5999   $247.60   $247.60   $247.60  
  Purchase #3 $214.81   7.147%   $230.1625   $230.16   $230.15   $230.20  
  Purchase #4 $87.74   7.858%   $94.6346   $94.63   $94.65   $94.60  
  Purchase #5 $20.99   7.279%   $22.5179   $22.52   $22.50   $22.50  
  Purchase #6 $232.74   5.250%   $244.9589   $244.96   $244.95   $245.00  
  Purchase #7 $102.57   3.665%   $106.3292   $106.33   $106.35   $106.30  
  7 purchase totals = $990.14       $1,065.7365   $1,065.73   $1,065.75   $1,065.70