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 $235.90   13.169%   $266.9657   $266.97   $266.95   $267.00  
  Purchase #2 $247.83   13.391%   $281.0169   $281.02   $281.00   $281.00  
  Purchase #3 $61.93   6.772%   $66.1239   $66.12   $66.10   $66.10  
  Purchase #4 $69.57   7.472%   $74.7683   $74.77   $74.75   $74.80  
  Purchase #5 $194.84   4.833%   $204.2566   $204.26   $204.25   $204.30  
  Purchase #6 $201.53   13.456%   $228.6479   $228.65   $228.65   $228.60  
  Purchase #7 $188.25   9.165%   $205.5031   $205.50   $205.50   $205.50  
  7 purchase totals = $1,199.85       $1,327.2824   $1,327.29   $1,327.20   $1,327.30