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 $63.27   8.310%   $68.5277   $68.53   $68.55   $68.50  
  Purchase #2 $202.62   10.474%   $223.8424   $223.84   $223.85   $223.80  
  Purchase #3 $216.86   4.141%   $225.8402   $225.84   $225.85   $225.80  
  Purchase #4 $34.41   13.162%   $38.939   $38.94   $38.95   $38.90  
  Purchase #5 $58.65   4.583%   $61.3379   $61.34   $61.35   $61.30  
  Purchase #6 $249.70   10.699%   $276.4154   $276.42   $276.40   $276.40  
  Purchase #7 $214.92   11.749%   $240.171   $240.17   $240.15   $240.20  
  7 purchase totals = $1,040.43       $1,135.0736   $1,135.08   $1,135.10   $1,134.90