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 $195.31   3.422%   $201.9935   $201.99   $202.00   $202.00  
  Purchase #2 $6.89   9.140%   $7.5197   $7.52   $7.50   $7.50  
  Purchase #3 $244.41   12.172%   $274.1596   $274.16   $274.15   $274.20  
  Purchase #4 $131.67   12.183%   $147.7114   $147.71   $147.70   $147.70  
  Purchase #5 $181.80   13.698%   $206.703   $206.70   $206.70   $206.70  
  Purchase #6 $165.35   9.230%   $180.6118   $180.61   $180.60   $180.60  
  Purchase #7 $55.33   3.465%   $57.2472   $57.25   $57.25   $57.20  
  7 purchase totals = $980.76       $1,075.9462   $1,075.94   $1,075.90   $1,075.90