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 $62.55   12.163%   $70.158   $70.16   $70.15   $70.20  
  Purchase #2 $109.39   5.783%   $115.716   $115.72   $115.70   $115.70  
  Purchase #3 $84.77   10.872%   $93.9862   $93.99   $94.00   $94.00  
  Purchase #4 $123.55   5.470%   $130.3082   $130.31   $130.30   $130.30  
  Purchase #5 $91.54   10.472%   $101.1261   $101.13   $101.15   $101.10  
  Purchase #6 $54.47   12.546%   $61.3038   $61.30   $61.30   $61.30  
  Purchase #7 $148.92   9.456%   $163.0019   $163.00   $163.00   $163.00  
  7 purchase totals = $675.19       $735.6002   $735.61   $735.60   $735.60