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 $125.77   3.385%   $130.0273   $130.03   $130.05   $130.00  
  Purchase #2 $60.96   7.646%   $65.621   $65.62   $65.60   $65.60  
  Purchase #3 $55.77   8.817%   $60.6872   $60.69   $60.70   $60.70  
  Purchase #4 $41.65   3.842%   $43.2502   $43.25   $43.25   $43.30  
  Purchase #5 $60.86   4.276%   $63.4624   $63.46   $63.45   $63.50  
  Purchase #6 $68.50   5.865%   $72.5175   $72.52   $72.50   $72.50  
  Purchase #7 $212.86   3.655%   $220.64   $220.64   $220.65   $220.60  
  7 purchase totals = $626.37       $656.2056   $656.21   $656.20   $656.20