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 $247.80   7.353%   $266.0207   $266.02   $266.00   $266.00  
  Purchase #2 $181.74   7.213%   $194.8489   $194.85   $194.85   $194.80  
  Purchase #3 $38.67   6.465%   $41.17   $41.17   $41.15   $41.20  
  Purchase #4 $65.98   7.381%   $70.85   $70.85   $70.85   $70.90  
  Purchase #5 $170.55   9.830%   $187.3151   $187.32   $187.30   $187.30  
  Purchase #6 $67.73   11.598%   $75.5853   $75.59   $75.60   $75.60  
  Purchase #7 $214.37   9.419%   $234.5615   $234.56   $234.55   $234.60  
  7 purchase totals = $986.84       $1,070.3515   $1,070.36   $1,070.30   $1,070.40