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 $169.97   13.576%   $193.0451   $193.05   $193.05   $193.00  
  Purchase #2 $185.57   9.661%   $203.4979   $203.50   $203.50   $203.50  
  Purchase #3 $225.84   13.859%   $257.1392   $257.14   $257.15   $257.10  
  Purchase #4 $181.79   11.456%   $202.6159   $202.62   $202.60   $202.60  
  Purchase #5 $22.42   8.136%   $24.2441   $24.24   $24.25   $24.20  
  Purchase #6 $148.78   5.240%   $156.5761   $156.58   $156.60   $156.60  
  Purchase #7 $85.41   3.703%   $88.5727   $88.57   $88.55   $88.60  
  7 purchase totals = $1,019.78       $1,125.6910   $1,125.70   $1,125.70   $1,125.60