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 $177.87   4.103%   $185.168   $185.17   $185.15   $185.20  
  Purchase #2 $81.35   12.433%   $91.4642   $91.46   $91.45   $91.50  
  Purchase #3 $36.36   9.513%   $39.8189   $39.82   $39.80   $39.80  
  Purchase #4 $237.86   13.329%   $269.5644   $269.56   $269.55   $269.60  
  Purchase #5 $95.30   13.107%   $107.791   $107.79   $107.80   $107.80  
  Purchase #6 $180.68   5.169%   $190.0193   $190.02   $190.00   $190.00  
  Purchase #7 $11.40   4.861%   $11.9542   $11.95   $11.95   $12.00  
  7 purchase totals = $820.82       $895.7800   $895.77   $895.70   $895.90