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 $248.96   6.349%   $264.7665   $264.77   $264.75   $264.80  
  Purchase #2 $132.92   9.563%   $145.6311   $145.63   $145.65   $145.60  
  Purchase #3 $65.55   6.718%   $69.9536   $69.95   $69.95   $70.00  
  Purchase #4 $95.42   11.399%   $106.2969   $106.30   $106.30   $106.30  
  Purchase #5 $239.64   9.869%   $263.2901   $263.29   $263.30   $263.30  
  Purchase #6 $97.88   8.645%   $106.3417   $106.34   $106.35   $106.30  
  Purchase #7 $233.59   12.719%   $263.3003   $263.30   $263.30   $263.30  
  7 purchase totals = $1,113.96       $1,219.5802   $1,219.58   $1,219.60   $1,219.60