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 $110.70   6.240%   $117.6077   $117.61   $117.60   $117.60  
  Purchase #2 $241.87   9.865%   $265.7305   $265.73   $265.75   $265.70  
  Purchase #3 $193.27   10.183%   $212.9507   $212.95   $212.95   $213.00  
  Purchase #4 $239.64   11.442%   $267.0596   $267.06   $267.05   $267.10  
  Purchase #5 $150.94   8.121%   $163.1978   $163.20   $163.20   $163.20  
  Purchase #6 $73.61   12.806%   $83.0365   $83.04   $83.05   $83.00  
  Purchase #7 $110.56   11.842%   $123.6525   $123.65   $123.65   $123.70  
  7 purchase totals = $1,120.59       $1,233.2353   $1,233.24   $1,233.25   $1,233.30