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 $212.58   13.717%   $241.7396   $241.74   $241.75   $241.70  
  Purchase #2 $77.95   8.792%   $84.8034   $84.80   $84.80   $84.80  
  Purchase #3 $74.72   10.742%   $82.7464   $82.75   $82.75   $82.70  
  Purchase #4 $244.48   11.269%   $272.0305   $272.03   $272.05   $272.00  
  Purchase #5 $101.36   5.422%   $106.8557   $106.86   $106.85   $106.90  
  Purchase #6 $176.62   5.873%   $186.9929   $186.99   $187.00   $187.00  
  Purchase #7 $163.53   5.763%   $172.9542   $172.95   $172.95   $173.00  
  7 purchase totals = $1,051.24       $1,148.1227   $1,148.12   $1,148.15   $1,148.10