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 $246.65   11.854%   $275.8879   $275.89   $275.90   $275.90  
  Purchase #2 $62.90   8.798%   $68.4339   $68.43   $68.45   $68.40  
  Purchase #3 $49.94   9.780%   $54.8241   $54.82   $54.80   $54.80  
  Purchase #4 $200.45   5.325%   $211.124   $211.12   $211.10   $211.10  
  Purchase #5 $227.76   8.467%   $247.0444   $247.04   $247.05   $247.00  
  Purchase #6 $58.87   5.487%   $62.1002   $62.10   $62.10   $62.10  
  Purchase #7 $157.81   11.156%   $175.4153   $175.42   $175.40   $175.40  
  7 purchase totals = $1,004.38       $1,094.8298   $1,094.82   $1,094.80   $1,094.70