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 $201.86   13.814%   $229.7449   $229.74   $229.75   $229.70  
  Purchase #2 $171.50   11.728%   $191.6135   $191.61   $191.60   $191.60  
  Purchase #3 $70.60   5.122%   $74.2161   $74.22   $74.20   $74.20  
  Purchase #4 $162.32   13.834%   $184.7753   $184.78   $184.80   $184.80  
  Purchase #5 $37.51   10.466%   $41.4358   $41.44   $41.45   $41.40  
  Purchase #6 $137.75   11.733%   $153.9122   $153.91   $153.90   $153.90  
  Purchase #7 $160.42   4.233%   $167.2106   $167.21   $167.20   $167.20  
  7 purchase totals = $941.96       $1,042.9084   $1,042.91   $1,042.90   $1,042.80