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 $210.82   6.289%   $224.0785   $224.08   $224.10   $224.10  
  Purchase #2 $156.49   3.552%   $162.0485   $162.05   $162.05   $162.00  
  Purchase #3 $6.82   7.630%   $7.3404   $7.34   $7.35   $7.30  
  Purchase #4 $98.47   6.131%   $104.5072   $104.51   $104.50   $104.50  
  Purchase #5 $193.91   5.573%   $204.7166   $204.72   $204.70   $204.70  
  Purchase #6 $205.58   5.459%   $216.8026   $216.80   $216.80   $216.80  
  Purchase #7 $84.73   11.792%   $94.7214   $94.72   $94.70   $94.70  
  7 purchase totals = $956.82       $1,014.2152   $1,014.22   $1,014.20   $1,014.10