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 $42.82   9.799%   $47.0159   $47.02   $47.00   $47.00  
  Purchase #2 $113.64   11.220%   $126.3904   $126.39   $126.40   $126.40  
  Purchase #3 $187.65   7.656%   $202.0165   $202.02   $202.00   $202.00  
  Purchase #4 $113.92   10.223%   $125.566   $125.57   $125.55   $125.60  
  Purchase #5 $201.87   9.634%   $221.3182   $221.32   $221.30   $221.30  
  Purchase #6 $66.80   9.275%   $72.9957   $73.00   $73.00   $73.00  
  Purchase #7 $249.99   6.759%   $266.8868   $266.89   $266.90   $266.90  
  7 purchase totals = $976.69       $1,062.1895   $1,062.21   $1,062.15   $1,062.20