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 $83.51   5.395%   $88.0154   $88.02   $88.00   $88.00  
  Purchase #2 $76.45   6.359%   $81.3115   $81.31   $81.30   $81.30  
  Purchase #3 $138.32   12.793%   $156.0153   $156.02   $156.00   $156.00  
  Purchase #4 $233.72   8.144%   $252.7542   $252.75   $252.75   $252.80  
  Purchase #5 $159.62   6.249%   $169.5947   $169.59   $169.60   $169.60  
  Purchase #6 $179.98   13.481%   $204.2431   $204.24   $204.25   $204.20  
  Purchase #7 $217.78   5.838%   $230.494   $230.49   $230.50   $230.50  
  7 purchase totals = $1,089.38       $1,182.4282   $1,182.42   $1,182.40   $1,182.40