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 $155.98   6.797%   $166.582   $166.58   $166.60   $166.60  
  Purchase #2 $113.32   11.335%   $126.1648   $126.16   $126.15   $126.20  
  Purchase #3 $164.43   8.220%   $177.9461   $177.95   $177.95   $177.90  
  Purchase #4 $154.31   12.437%   $173.5015   $173.50   $173.50   $173.50  
  Purchase #5 $205.34   6.676%   $219.0485   $219.05   $219.05   $219.00  
  Purchase #6 $56.32   4.612%   $58.9175   $58.92   $58.90   $58.90  
  Purchase #7 $145.74   13.559%   $165.5009   $165.50   $165.50   $165.50  
  7 purchase totals = $995.44       $1,087.6613   $1,087.66   $1,087.65   $1,087.60