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 $204.73   10.650%   $226.5337   $226.53   $226.55   $226.50  
  Purchase #2 $5.70   9.487%   $6.2408   $6.24   $6.25   $6.20  
  Purchase #3 $83.52   11.851%   $93.418   $93.42   $93.40   $93.40  
  Purchase #4 $247.29   12.409%   $277.9762   $277.98   $278.00   $278.00  
  Purchase #5 $238.85   7.168%   $255.9708   $255.97   $255.95   $256.00  
  Purchase #6 $115.87   5.107%   $121.7875   $121.79   $121.80   $121.80  
  Purchase #7 $169.63   9.856%   $186.3487   $186.35   $186.35   $186.30  
  7 purchase totals = $1,065.59       $1,168.2757   $1,168.28   $1,168.30   $1,168.20