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 $59.72   10.162%   $65.7887   $65.79   $65.80   $65.80  
  Purchase #2 $224.91   3.264%   $232.2511   $232.25   $232.25   $232.30  
  Purchase #3 $54.65   10.818%   $60.562   $60.56   $60.55   $60.60  
  Purchase #4 $199.58   8.776%   $217.0951   $217.10   $217.10   $217.10  
  Purchase #5 $131.64   7.302%   $141.2524   $141.25   $141.25   $141.30  
  Purchase #6 $191.66   4.495%   $200.2751   $200.28   $200.30   $200.30  
  Purchase #7 $88.51   10.414%   $97.7274   $97.73   $97.75   $97.70  
  7 purchase totals = $950.67       $1,014.9518   $1,014.96   $1,015.00   $1,015.10