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 $39.41   13.163%   $44.5975   $44.60   $44.60   $44.60  
  Purchase #2 $68.30   9.353%   $74.6881   $74.69   $74.70   $74.70  
  Purchase #3 $211.25   11.265%   $235.0473   $235.05   $235.05   $235.00  
  Purchase #4 $221.50   11.405%   $246.7621   $246.76   $246.75   $246.80  
  Purchase #5 $221.31   10.107%   $243.6778   $243.68   $243.70   $243.70  
  Purchase #6 $59.85   11.235%   $66.5741   $66.57   $66.55   $66.60  
  Purchase #7 $181.54   7.254%   $194.7089   $194.71   $194.70   $194.70  
  7 purchase totals = $1,003.16       $1,106.0558   $1,106.06   $1,106.05   $1,106.10