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 $38.52   6.833%   $41.1521   $41.15   $41.15   $41.20  
  Purchase #2 $184.93   5.601%   $195.2879   $195.29   $195.30   $195.30  
  Purchase #3 $219.87   6.735%   $234.6782   $234.68   $234.70   $234.70  
  Purchase #4 $215.45   3.485%   $222.9584   $222.96   $222.95   $223.00  
  Purchase #5 $120.93   6.300%   $128.5486   $128.55   $128.55   $128.50  
  Purchase #6 $149.29   10.162%   $164.4608   $164.46   $164.45   $164.50  
  Purchase #7 $58.38   9.478%   $63.9133   $63.91   $63.90   $63.90  
  7 purchase totals = $987.37       $1,050.9993   $1,051.00   $1,051.00   $1,051.10