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 $45.35   11.798%   $50.7004   $50.70   $50.70   $50.70  
  Purchase #2 $235.47   3.233%   $243.0827   $243.08   $243.10   $243.10  
  Purchase #3 $96.88   12.428%   $108.9202   $108.92   $108.90   $108.90  
  Purchase #4 $223.41   4.325%   $233.0725   $233.07   $233.05   $233.10  
  Purchase #5 $179.68   10.109%   $197.8439   $197.84   $197.85   $197.80  
  Purchase #6 $170.73   3.667%   $176.9907   $176.99   $177.00   $177.00  
  Purchase #7 $233.39   13.175%   $264.1391   $264.14   $264.15   $264.10  
  7 purchase totals = $1,184.91       $1,274.7495   $1,274.74   $1,274.75   $1,274.70