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 $48.98   13.562%   $55.6227   $55.62   $55.60   $55.60  
  Purchase #2 $155.66   11.759%   $173.9641   $173.96   $173.95   $174.00  
  Purchase #3 $223.40   5.568%   $235.8389   $235.84   $235.85   $235.80  
  Purchase #4 $184.61   12.369%   $207.4444   $207.44   $207.45   $207.40  
  Purchase #5 $138.69   12.784%   $156.4201   $156.42   $156.40   $156.40  
  Purchase #6 $179.28   9.701%   $196.672   $196.67   $196.65   $196.70  
  Purchase #7 $197.58   5.764%   $208.9685   $208.97   $208.95   $209.00  
  7 purchase totals = $1,128.20       $1,234.9307   $1,234.92   $1,234.85   $1,234.90