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 $171.56   12.848%   $193.602   $193.60   $193.60   $193.60  
  Purchase #2 $92.76   5.547%   $97.9054   $97.91   $97.90   $97.90  
  Purchase #3 $165.48   6.505%   $176.2445   $176.24   $176.25   $176.20  
  Purchase #4 $204.30   12.585%   $230.0112   $230.01   $230.00   $230.00  
  Purchase #5 $104.92   13.109%   $118.674   $118.67   $118.65   $118.70  
  Purchase #6 $191.75   5.867%   $203   $203.00   $203.00   $203.00  
  Purchase #7 $92.45   4.236%   $96.3662   $96.37   $96.35   $96.40  
  7 purchase totals = $1,023.22       $1,115.8033   $1,115.80   $1,115.75   $1,115.80