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 $73.68   7.162%   $78.957   $78.96   $78.95   $79.00  
  Purchase #2 $24.96   7.641%   $26.8672   $26.87   $26.85   $26.90  
  Purchase #3 $140.91   3.327%   $145.5981   $145.60   $145.60   $145.60  
  Purchase #4 $111.26   13.205%   $125.9519   $125.95   $125.95   $126.00  
  Purchase #5 $99.64   7.565%   $107.1778   $107.18   $107.20   $107.20  
  Purchase #6 $206.99   5.146%   $217.6417   $217.64   $217.65   $217.60  
  Purchase #7 $44.82   8.487%   $48.6239   $48.62   $48.60   $48.60  
  7 purchase totals = $702.26       $750.8176   $750.82   $750.80   $750.90