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 $171.37   13.465%   $194.445   $194.45   $194.45   $194.40  
  Purchase #2 $235.82   4.281%   $245.9155   $245.92   $245.90   $245.90  
  Purchase #3 $60.94   6.544%   $64.9279   $64.93   $64.95   $64.90  
  Purchase #4 $13.59   8.191%   $14.7032   $14.70   $14.70   $14.70  
  Purchase #5 $78.67   6.574%   $83.8418   $83.84   $83.85   $83.80  
  Purchase #6 $163.97   6.288%   $174.2804   $174.28   $174.30   $174.30  
  Purchase #7 $39.73   8.349%   $43.0471   $43.05   $43.05   $43.00  
  7 purchase totals = $764.09       $821.1609   $821.17   $821.20   $821.00