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 $228.88   5.693%   $241.9101   $241.91   $241.90   $241.90  
  Purchase #2 $65.36   4.483%   $68.2901   $68.29   $68.30   $68.30  
  Purchase #3 $202.96   7.481%   $218.1434   $218.14   $218.15   $218.10  
  Purchase #4 $134.65   12.282%   $151.1877   $151.19   $151.20   $151.20  
  Purchase #5 $181.81   8.523%   $197.3057   $197.31   $197.30   $197.30  
  Purchase #6 $20.46   3.519%   $21.18   $21.18   $21.20   $21.20  
  Purchase #7 $97.59   7.187%   $104.6038   $104.60   $104.60   $104.60  
  7 purchase totals = $931.71       $1,002.6208   $1,002.62   $1,002.65   $1,002.60