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 $184.44   9.698%   $202.327   $202.33   $202.35   $202.30  
  Purchase #2 $140.79   6.592%   $150.0709   $150.07   $150.05   $150.10  
  Purchase #3 $14.42   7.660%   $15.5246   $15.52   $15.50   $15.50  
  Purchase #4 $70.51   3.778%   $73.1739   $73.17   $73.15   $73.20  
  Purchase #5 $29.68   13.760%   $33.764   $33.76   $33.75   $33.80  
  Purchase #6 $246.69   8.553%   $267.7894   $267.79   $267.80   $267.80  
  Purchase #7 $236.77   11.714%   $264.5052   $264.51   $264.50   $264.50  
  7 purchase totals = $923.30       $1,007.1550   $1,007.15   $1,007.10   $1,007.20