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 $196.56   5.596%   $207.5595   $207.56   $207.55   $207.60  
  Purchase #2 $247.87   4.323%   $258.5854   $258.59   $258.60   $258.60  
  Purchase #3 $165.70   8.589%   $179.932   $179.93   $179.95   $179.90  
  Purchase #4 $197.39   3.305%   $203.9137   $203.91   $203.90   $203.90  
  Purchase #5 $110.57   9.414%   $120.9791   $120.98   $121.00   $121.00  
  Purchase #6 $134.53   8.558%   $146.0431   $146.04   $146.05   $146.00  
  Purchase #7 $228.46   9.780%   $250.8034   $250.80   $250.80   $250.80  
  7 purchase totals = $1,281.08       $1,367.8162   $1,367.81   $1,367.85   $1,367.80