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 $108.67   8.171%   $117.5494   $117.55   $117.55   $117.50  
  Purchase #2 $189.78   5.856%   $200.8935   $200.89   $200.90   $200.90  
  Purchase #3 $171.57   7.123%   $183.7909   $183.79   $183.80   $183.80  
  Purchase #4 $65.56   6.386%   $69.7467   $69.75   $69.75   $69.70  
  Purchase #5 $212.41   6.207%   $225.5943   $225.59   $225.60   $225.60  
  Purchase #6 $181.42   5.337%   $191.1024   $191.10   $191.10   $191.10  
  Purchase #7 $39.81   9.683%   $43.6648   $43.66   $43.65   $43.70  
  7 purchase totals = $969.22       $1,032.3420   $1,032.33   $1,032.35   $1,032.30