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 $66.75   11.681%   $74.5471   $74.55   $74.55   $74.50  
  Purchase #2 $216.50   10.373%   $238.9575   $238.96   $238.95   $239.00  
  Purchase #3 $65.59   12.607%   $73.8589   $73.86   $73.85   $73.90  
  Purchase #4 $181.60   11.677%   $202.8054   $202.81   $202.80   $202.80  
  Purchase #5 $177.49   13.487%   $201.4281   $201.43   $201.45   $201.40  
  Purchase #6 $211.28   5.641%   $223.1983   $223.20   $223.20   $223.20  
  Purchase #7 $119.46   11.424%   $133.1071   $133.11   $133.10   $133.10  
  7 purchase totals = $1,038.67       $1,147.9024   $1,147.92   $1,147.90   $1,147.90