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 $204.76   11.653%   $228.6207   $228.62   $228.60   $228.60  
  Purchase #2 $17.87   6.753%   $19.0768   $19.08   $19.10   $19.10  
  Purchase #3 $234.39   5.283%   $246.7728   $246.77   $246.75   $246.80  
  Purchase #4 $87.90   6.215%   $93.363   $93.36   $93.35   $93.40  
  Purchase #5 $216.46   3.115%   $223.2027   $223.20   $223.20   $223.20  
  Purchase #6 $136.58   4.605%   $142.8695   $142.87   $142.85   $142.90  
  Purchase #7 $63.53   6.201%   $67.4695   $67.47   $67.45   $67.50  
  7 purchase totals = $961.49       $1,021.3750   $1,021.37   $1,021.30   $1,021.50