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 $60.42   11.427%   $67.3242   $67.32   $67.30   $67.30  
  Purchase #2 $211.96   7.518%   $227.8952   $227.90   $227.90   $227.90  
  Purchase #3 $165.45   9.687%   $181.4771   $181.48   $181.50   $181.50  
  Purchase #4 $38.63   9.671%   $42.3659   $42.37   $42.35   $42.40  
  Purchase #5 $201.73   9.760%   $221.4188   $221.42   $221.40   $221.40  
  Purchase #6 $110.70   13.461%   $125.6013   $125.60   $125.60   $125.60  
  Purchase #7 $24.45   13.848%   $27.8358   $27.84   $27.85   $27.80  
  7 purchase totals = $813.34       $893.9183   $893.93   $893.90   $893.90