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 $53.46   10.206%   $58.9161   $58.92   $58.90   $58.90  
  Purchase #2 $244.28   6.373%   $259.848   $259.85   $259.85   $259.80  
  Purchase #3 $43.99   10.300%   $48.521   $48.52   $48.50   $48.50  
  Purchase #4 $36.34   3.473%   $37.6021   $37.60   $37.60   $37.60  
  Purchase #5 $24.89   3.668%   $25.803   $25.80   $25.80   $25.80  
  Purchase #6 $183.85   5.366%   $193.7154   $193.72   $193.70   $193.70  
  Purchase #7 $198.26   6.374%   $210.8971   $210.90   $210.90   $210.90  
  7 purchase totals = $785.07       $835.3027   $835.31   $835.25   $835.20