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 $202.50   10.539%   $223.8415   $223.84   $223.85   $223.80  
  Purchase #2 $140.61   11.251%   $156.43   $156.43   $156.45   $156.40  
  Purchase #3 $33.88   6.764%   $36.1716   $36.17   $36.15   $36.20  
  Purchase #4 $247.86   5.829%   $262.3078   $262.31   $262.30   $262.30  
  Purchase #5 $219.49   12.828%   $247.6462   $247.65   $247.65   $247.60  
  Purchase #6 $200.64   12.287%   $225.2926   $225.29   $225.30   $225.30  
  Purchase #7 $118.40   10.203%   $130.4804   $130.48   $130.50   $130.50  
  7 purchase totals = $1,163.38       $1,282.1701   $1,282.17   $1,282.20   $1,282.10