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 $102.56   10.541%   $113.3708   $113.37   $113.35   $113.40  
  Purchase #2 $112.79   3.626%   $116.8798   $116.88   $116.90   $116.90  
  Purchase #3 $220.52   4.824%   $231.1579   $231.16   $231.15   $231.20  
  Purchase #4 $224.67   11.609%   $250.7519   $250.75   $250.75   $250.80  
  Purchase #5 $56.91   9.218%   $62.156   $62.16   $62.15   $62.20  
  Purchase #6 $181.72   6.670%   $193.8407   $193.84   $193.85   $193.80  
  Purchase #7 $220.55   6.573%   $235.0468   $235.05   $235.05   $235.00  
  7 purchase totals = $1,119.72       $1,203.2039   $1,203.21   $1,203.20   $1,203.30