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 $83.94   9.599%   $91.9974   $92.00   $92.00   $92.00  
  Purchase #2 $235.67   12.661%   $265.5082   $265.51   $265.50   $265.50  
  Purchase #3 $88.73   10.144%   $97.7308   $97.73   $97.75   $97.70  
  Purchase #4 $153.47   11.268%   $170.763   $170.76   $170.75   $170.80  
  Purchase #5 $109.56   10.345%   $120.894   $120.89   $120.90   $120.90  
  Purchase #6 $197.76   10.659%   $218.8392   $218.84   $218.85   $218.80  
  Purchase #7 $151.83   4.740%   $159.0267   $159.03   $159.05   $159.00  
  7 purchase totals = $1,020.96       $1,124.7593   $1,124.76   $1,124.80   $1,124.70