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 $54.63   3.521%   $56.5535   $56.55   $56.55   $56.60  
  Purchase #2 $102.72   6.294%   $109.1852   $109.19   $109.20   $109.20  
  Purchase #3 $66.54   10.712%   $73.6678   $73.67   $73.65   $73.70  
  Purchase #4 $198.57   6.183%   $210.8476   $210.85   $210.85   $210.80  
  Purchase #5 $247.71   8.423%   $268.5746   $268.57   $268.55   $268.60  
  Purchase #6 $246.74   8.594%   $267.9448   $267.94   $267.95   $267.90  
  Purchase #7 $24.49   9.546%   $26.8278   $26.83   $26.85   $26.80  
  7 purchase totals = $941.40       $1,013.6013   $1,013.60   $1,013.60   $1,013.60