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 $91.64   11.702%   $102.3637   $102.36   $102.35   $102.40  
  Purchase #2 $235.78   5.379%   $248.4626   $248.46   $248.45   $248.50  
  Purchase #3 $234.89   12.592%   $264.4673   $264.47   $264.45   $264.50  
  Purchase #4 $112.83   3.462%   $116.7362   $116.74   $116.75   $116.70  
  Purchase #5 $77.74   4.570%   $81.2927   $81.29   $81.30   $81.30  
  Purchase #6 $169.81   10.649%   $187.8931   $187.89   $187.90   $187.90  
  Purchase #7 $39.70   3.332%   $41.0228   $41.02   $41.00   $41.00  
  7 purchase totals = $962.39       $1,042.2384   $1,042.23   $1,042.20   $1,042.30