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 $87.68   4.613%   $91.7247   $91.72   $91.70   $91.70  
  Purchase #2 $124.67   11.760%   $139.3312   $139.33   $139.35   $139.30  
  Purchase #3 $78.98   5.364%   $83.2165   $83.22   $83.20   $83.20  
  Purchase #4 $68.64   6.620%   $73.184   $73.18   $73.20   $73.20  
  Purchase #5 $224.74   9.720%   $246.5847   $246.58   $246.60   $246.60  
  Purchase #6 $49.82   4.499%   $52.0614   $52.06   $52.05   $52.10  
  Purchase #7 $65.41   7.171%   $70.1006   $70.10   $70.10   $70.10  
  7 purchase totals = $699.94       $756.2031   $756.19   $756.20   $756.20