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 $168.59   13.411%   $191.1996   $191.20   $191.20   $191.20  
  Purchase #2 $229.40   7.601%   $246.8367   $246.84   $246.85   $246.80  
  Purchase #3 $25.93   7.451%   $27.862   $27.86   $27.85   $27.90  
  Purchase #4 $193.76   9.435%   $212.0413   $212.04   $212.05   $212.00  
  Purchase #5 $222.40   5.647%   $234.9589   $234.96   $234.95   $235.00  
  Purchase #6 $179.80   13.255%   $203.6325   $203.63   $203.65   $203.60  
  Purchase #7 $70.54   3.327%   $72.8869   $72.89   $72.90   $72.90  
  7 purchase totals = $1,090.42       $1,189.4179   $1,189.42   $1,189.45   $1,189.40