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 $97.61   7.121%   $104.5608   $104.56   $104.55   $104.60  
  Purchase #2 $181.73   10.194%   $200.2556   $200.26   $200.25   $200.30  
  Purchase #3 $34.82   5.736%   $36.8173   $36.82   $36.80   $36.80  
  Purchase #4 $204.49   11.467%   $227.9389   $227.94   $227.95   $227.90  
  Purchase #5 $89.35   8.545%   $96.985   $96.99   $97.00   $97.00  
  Purchase #6 $186.59   13.766%   $212.276   $212.28   $212.30   $212.30  
  Purchase #7 $189.47   7.434%   $203.5552   $203.56   $203.55   $203.60  
  7 purchase totals = $984.06       $1,082.3888   $1,082.41   $1,082.40   $1,082.50