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 $49.41   13.259%   $55.9613   $55.96   $55.95   $56.00  
  Purchase #2 $134.35   11.792%   $150.1926   $150.19   $150.20   $150.20  
  Purchase #3 $152.65   6.771%   $162.9859   $162.99   $163.00   $163.00  
  Purchase #4 $141.80   13.778%   $161.3372   $161.34   $161.35   $161.30  
  Purchase #5 $135.75   13.723%   $154.379   $154.38   $154.40   $154.40  
  Purchase #6 $201.65   11.685%   $225.2128   $225.21   $225.20   $225.20  
  Purchase #7 $194.94   9.104%   $212.6873   $212.69   $212.70   $212.70  
  7 purchase totals = $1,010.55       $1,122.7561   $1,122.76   $1,122.80   $1,122.80