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 $146.52   9.175%   $159.9632   $159.96   $159.95   $160.00  
  Purchase #2 $128.32   5.265%   $135.076   $135.08   $135.10   $135.10  
  Purchase #3 $184.90   3.704%   $191.7487   $191.75   $191.75   $191.70  
  Purchase #4 $16.72   12.158%   $18.7528   $18.75   $18.75   $18.80  
  Purchase #5 $88.53   10.820%   $98.1089   $98.11   $98.10   $98.10  
  Purchase #6 $29.95   9.691%   $32.8525   $32.85   $32.85   $32.90  
  Purchase #7 $13.30   8.351%   $14.4107   $14.41   $14.40   $14.40  
  7 purchase totals = $608.24       $650.9128   $650.91   $650.90   $651.00