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 $43.86   11.847%   $49.0561   $49.06   $49.05   $49.10  
  Purchase #2 $229.46   11.372%   $255.5542   $255.55   $255.55   $255.60  
  Purchase #3 $152.30   10.283%   $167.961   $167.96   $167.95   $168.00  
  Purchase #4 $82.62   6.610%   $88.0812   $88.08   $88.10   $88.10  
  Purchase #5 $193.62   4.416%   $202.1703   $202.17   $202.15   $202.20  
  Purchase #6 $97.42   3.358%   $100.6914   $100.69   $100.70   $100.70  
  Purchase #7 $154.27   10.625%   $170.6612   $170.66   $170.65   $170.70  
  7 purchase totals = $953.55       $1,034.1754   $1,034.17   $1,034.15   $1,034.40