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 $226.59   8.150%   $245.0571   $245.06   $245.05   $245.10  
  Purchase #2 $212.58   9.487%   $232.7475   $232.75   $232.75   $232.70  
  Purchase #3 $193.82   12.641%   $218.3208   $218.32   $218.30   $218.30  
  Purchase #4 $52.51   6.371%   $55.8554   $55.86   $55.85   $55.90  
  Purchase #5 $174.34   4.135%   $181.549   $181.55   $181.55   $181.50  
  Purchase #6 $101.53   6.342%   $107.969   $107.97   $107.95   $108.00  
  Purchase #7 $191.89   4.771%   $201.0451   $201.05   $201.05   $201.00  
  7 purchase totals = $1,153.26       $1,242.5439   $1,242.56   $1,242.50   $1,242.50