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 $218.47   12.819%   $246.4757   $246.48   $246.50   $246.50  
  Purchase #2 $143.32   11.340%   $159.5725   $159.57   $159.55   $159.60  
  Purchase #3 $66.64   3.131%   $68.7265   $68.73   $68.75   $68.70  
  Purchase #4 $38.39   11.449%   $42.7853   $42.79   $42.80   $42.80  
  Purchase #5 $240.78   10.428%   $265.8885   $265.89   $265.90   $265.90  
  Purchase #6 $152.55   8.226%   $165.0988   $165.10   $165.10   $165.10  
  Purchase #7 $184.90   10.405%   $204.1388   $204.14   $204.15   $204.10  
  7 purchase totals = $1,045.05       $1,152.6861   $1,152.70   $1,152.75   $1,152.70