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 $55.73   12.164%   $62.509   $62.51   $62.50   $62.50  
  Purchase #2 $36.75   11.365%   $40.9266   $40.93   $40.95   $40.90  
  Purchase #3 $206.89   5.364%   $217.9876   $217.99   $218.00   $218.00  
  Purchase #4 $233.74   7.743%   $251.8385   $251.84   $251.85   $251.80  
  Purchase #5 $201.78   12.716%   $227.4383   $227.44   $227.45   $227.40  
  Purchase #6 $94.45   6.585%   $100.6695   $100.67   $100.65   $100.70  
  Purchase #7 $160.52   3.847%   $166.6952   $166.70   $166.70   $166.70  
  7 purchase totals = $989.86       $1,068.0647   $1,068.08   $1,068.10   $1,068.00