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 $126.29   5.118%   $132.7535   $132.75   $132.75   $132.80  
  Purchase #2 $142.36   5.793%   $150.6069   $150.61   $150.60   $150.60  
  Purchase #3 $213.72   5.128%   $224.6796   $224.68   $224.70   $224.70  
  Purchase #4 $245.97   11.166%   $273.435   $273.44   $273.45   $273.40  
  Purchase #5 $96.55   12.218%   $108.3465   $108.35   $108.35   $108.30  
  Purchase #6 $192.96   12.424%   $216.9334   $216.93   $216.95   $216.90  
  Purchase #7 $86.93   9.402%   $95.1032   $95.10   $95.10   $95.10  
  7 purchase totals = $1,104.78       $1,201.8581   $1,201.86   $1,201.90   $1,201.80