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 $99.70   13.692%   $113.3509   $113.35   $113.35   $113.40  
  Purchase #2 $13.64   8.387%   $14.784   $14.78   $14.80   $14.80  
  Purchase #3 $180.27   10.496%   $199.1911   $199.19   $199.20   $199.20  
  Purchase #4 $219.65   7.868%   $236.9321   $236.93   $236.95   $236.90  
  Purchase #5 $131.94   13.155%   $149.2967   $149.30   $149.30   $149.30  
  Purchase #6 $136.71   11.704%   $152.7105   $152.71   $152.70   $152.70  
  Purchase #7 $243.48   10.120%   $268.1202   $268.12   $268.10   $268.10  
  7 purchase totals = $1,025.39       $1,134.3855   $1,134.38   $1,134.40   $1,134.40