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 $177.60   13.641%   $201.8264   $201.83   $201.85   $201.80  
  Purchase #2 $243.62   13.524%   $276.5672   $276.57   $276.55   $276.60  
  Purchase #3 $97.69   12.452%   $109.8544   $109.85   $109.85   $109.90  
  Purchase #4 $102.79   11.813%   $114.9326   $114.93   $114.95   $114.90  
  Purchase #5 $31.86   13.316%   $36.1025   $36.10   $36.10   $36.10  
  Purchase #6 $194.33   9.362%   $212.5232   $212.52   $212.50   $212.50  
  Purchase #7 $247.33   6.304%   $262.9217   $262.92   $262.90   $262.90  
  7 purchase totals = $1,095.22       $1,214.7280   $1,214.72   $1,214.70   $1,214.70