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 $185.67   11.571%   $207.1539   $207.15   $207.15   $207.20  
  Purchase #2 $39.78   13.839%   $45.2852   $45.29   $45.30   $45.30  
  Purchase #3 $215.43   13.313%   $244.1102   $244.11   $244.10   $244.10  
  Purchase #4 $160.63   13.125%   $181.7127   $181.71   $181.70   $181.70  
  Purchase #5 $95.47   6.390%   $101.5705   $101.57   $101.55   $101.60  
  Purchase #6 $113.90   6.597%   $121.414   $121.41   $121.40   $121.40  
  Purchase #7 $162.96   7.204%   $174.6996   $174.70   $174.70   $174.70  
  7 purchase totals = $973.84       $1,075.9461   $1,075.94   $1,075.90   $1,076.00