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 $119.73   12.333%   $134.4963   $134.50   $134.50   $134.50  
  Purchase #2 $91.97   6.452%   $97.9039   $97.90   $97.90   $97.90  
  Purchase #3 $84.90   3.418%   $87.8019   $87.80   $87.80   $87.80  
  Purchase #4 $149.51   7.172%   $160.2329   $160.23   $160.25   $160.20  
  Purchase #5 $91.75   7.540%   $98.668   $98.67   $98.65   $98.70  
  Purchase #6 $220.48   6.712%   $235.2786   $235.28   $235.30   $235.30  
  Purchase #7 $202.53   8.664%   $220.0772   $220.08   $220.10   $220.10  
  7 purchase totals = $960.87       $1,034.4588   $1,034.46   $1,034.50   $1,034.50