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 $198.94   13.861%   $226.5151   $226.52   $226.50   $226.50  
  Purchase #2 $220.92   6.807%   $235.958   $235.96   $235.95   $236.00  
  Purchase #3 $52.65   11.677%   $58.7979   $58.80   $58.80   $58.80  
  Purchase #4 $92.85   11.148%   $103.2009   $103.20   $103.20   $103.20  
  Purchase #5 $100.30   3.693%   $104.0041   $104.00   $104.00   $104.00  
  Purchase #6 $118.96   7.865%   $128.3162   $128.32   $128.30   $128.30  
  Purchase #7 $205.36   7.822%   $221.4233   $221.42   $221.40   $221.40  
  7 purchase totals = $989.98       $1,078.2155   $1,078.22   $1,078.15   $1,078.20