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 $184.82   11.345%   $205.7878   $205.79   $205.80   $205.80  
  Purchase #2 $116.75   5.276%   $122.9097   $122.91   $122.90   $122.90  
  Purchase #3 $189.83   5.309%   $199.9081   $199.91   $199.90   $199.90  
  Purchase #4 $150.60   11.178%   $167.4341   $167.43   $167.45   $167.40  
  Purchase #5 $13.98   11.714%   $15.6176   $15.62   $15.60   $15.60  
  Purchase #6 $130.53   5.871%   $138.1934   $138.19   $138.20   $138.20  
  Purchase #7 $117.35   7.789%   $126.4904   $126.49   $126.50   $126.50  
  7 purchase totals = $903.86       $976.3411   $976.34   $976.35   $976.30