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 $67.42   11.730%   $75.3284   $75.33   $75.35   $75.30  
  Purchase #2 $44.58   13.538%   $50.6152   $50.62   $50.60   $50.60  
  Purchase #3 $181.74   10.153%   $200.1921   $200.19   $200.20   $200.20  
  Purchase #4 $98.92   9.753%   $108.5677   $108.57   $108.55   $108.60  
  Purchase #5 $107.72   4.814%   $112.9056   $112.91   $112.90   $112.90  
  Purchase #6 $234.53   12.566%   $264.001   $264.00   $264.00   $264.00  
  Purchase #7 $189.93   12.145%   $212.997   $213.00   $213.00   $213.00  
  7 purchase totals = $924.84       $1,024.6070   $1,024.62   $1,024.60   $1,024.60