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 $226.30   9.378%   $247.5224   $247.52   $247.50   $247.50  
  Purchase #2 $87.72   8.182%   $94.8973   $94.90   $94.90   $94.90  
  Purchase #3 $79.58   13.535%   $90.3512   $90.35   $90.35   $90.40  
  Purchase #4 $148.96   5.404%   $157.0098   $157.01   $157.00   $157.00  
  Purchase #5 $60.90   12.210%   $68.3359   $68.34   $68.35   $68.30  
  Purchase #6 $247.47   8.799%   $269.2449   $269.24   $269.25   $269.20  
  Purchase #7 $8.56   5.280%   $9.012   $9.01   $9.00   $9.00  
  7 purchase totals = $859.49       $936.3735   $936.37   $936.35   $936.30