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 $106.97   6.217%   $113.6203   $113.62   $113.60   $113.60  
  Purchase #2 $226.50   6.613%   $241.4784   $241.48   $241.50   $241.50  
  Purchase #3 $220.82   7.293%   $236.9244   $236.92   $236.90   $236.90  
  Purchase #4 $145.56   3.735%   $150.9967   $151.00   $151.00   $151.00  
  Purchase #5 $209.80   11.331%   $233.5724   $233.57   $233.55   $233.60  
  Purchase #6 $21.97   12.561%   $24.7297   $24.73   $24.75   $24.70  
  Purchase #7 $165.66   5.573%   $174.8922   $174.89   $174.90   $174.90  
  7 purchase totals = $1,097.28       $1,176.2141   $1,176.21   $1,176.20   $1,176.20