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 $123.38   9.179%   $134.7051   $134.71   $134.70   $134.70  
  Purchase #2 $228.63   6.664%   $243.8659   $243.87   $243.85   $243.90  
  Purchase #3 $179.78   9.556%   $196.9598   $196.96   $196.95   $197.00  
  Purchase #4 $36.44   7.546%   $39.1898   $39.19   $39.20   $39.20  
  Purchase #5 $53.50   5.416%   $56.3976   $56.40   $56.40   $56.40  
  Purchase #6 $203.91   10.393%   $225.1024   $225.10   $225.10   $225.10  
  Purchase #7 $202.50   10.791%   $224.3518   $224.35   $224.35   $224.40  
  7 purchase totals = $1,028.14       $1,120.5724   $1,120.58   $1,120.55   $1,120.70