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 $202.77   3.858%   $210.5929   $210.59   $210.60   $210.60  
  Purchase #2 $151.42   11.148%   $168.3003   $168.30   $168.30   $168.30  
  Purchase #3 $226.96   5.142%   $238.6303   $238.63   $238.65   $238.60  
  Purchase #4 $56.33   6.651%   $60.0765   $60.08   $60.10   $60.10  
  Purchase #5 $60.26   7.515%   $64.7885   $64.79   $64.80   $64.80  
  Purchase #6 $12.98   11.720%   $14.5013   $14.50   $14.50   $14.50  
  Purchase #7 $64.72   9.442%   $70.8309   $70.83   $70.85   $70.80  
  7 purchase totals = $775.44       $827.7207   $827.72   $827.80   $827.70