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 $231.67   11.707%   $258.7916   $258.79   $258.80   $258.80  
  Purchase #2 $135.68   11.280%   $150.9847   $150.98   $151.00   $151.00  
  Purchase #3 $45.45   13.371%   $51.5271   $51.53   $51.55   $51.50  
  Purchase #4 $149.52   8.280%   $161.9003   $161.90   $161.90   $161.90  
  Purchase #5 $98.87   8.413%   $107.1879   $107.19   $107.20   $107.20  
  Purchase #6 $69.34   4.275%   $72.3043   $72.30   $72.30   $72.30  
  Purchase #7 $233.49   10.423%   $257.8267   $257.83   $257.85   $257.80  
  7 purchase totals = $964.02       $1,060.5226   $1,060.52   $1,060.60   $1,060.50