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 $219.85   12.383%   $247.074   $247.07   $247.05   $247.10  
  Purchase #2 $177.80   7.421%   $190.9945   $190.99   $191.00   $191.00  
  Purchase #3 $44.98   5.339%   $47.3815   $47.38   $47.40   $47.40  
  Purchase #4 $230.88   6.599%   $246.1158   $246.12   $246.10   $246.10  
  Purchase #5 $165.99   8.874%   $180.72   $180.72   $180.70   $180.70  
  Purchase #6 $172.34   8.681%   $187.3008   $187.30   $187.30   $187.30  
  Purchase #7 $22.91   4.831%   $24.0168   $24.02   $24.00   $24.00  
  7 purchase totals = $1,034.75       $1,123.6034   $1,123.60   $1,123.55   $1,123.60