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 $204.40   12.211%   $229.3593   $229.36   $229.35   $229.40  
  Purchase #2 $39.49   3.716%   $40.9574   $40.96   $40.95   $41.00  
  Purchase #3 $160.48   4.151%   $167.1415   $167.14   $167.15   $167.10  
  Purchase #4 $127.53   3.744%   $132.3047   $132.30   $132.30   $132.30  
  Purchase #5 $202.99   4.225%   $211.5663   $211.57   $211.55   $211.60  
  Purchase #6 $244.80   9.219%   $267.3681   $267.37   $267.35   $267.40  
  Purchase #7 $193.86   3.690%   $201.0134   $201.01   $201.00   $201.00  
  7 purchase totals = $1,173.55       $1,249.7107   $1,249.71   $1,249.65   $1,249.80