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 $49.95   7.198%   $53.5454   $53.55   $53.55   $53.50  
  Purchase #2 $181.97   5.313%   $191.6381   $191.64   $191.65   $191.60  
  Purchase #3 $246.79   9.667%   $270.6472   $270.65   $270.65   $270.60  
  Purchase #4 $54.82   7.595%   $58.9836   $58.98   $59.00   $59.00  
  Purchase #5 $177.66   11.519%   $198.1247   $198.12   $198.10   $198.10  
  Purchase #6 $147.74   8.610%   $160.4604   $160.46   $160.45   $160.50  
  Purchase #7 $115.45   9.737%   $126.6914   $126.69   $126.70   $126.70  
  7 purchase totals = $974.38       $1,060.0908   $1,060.09   $1,060.10   $1,060.00