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 $24.43   5.790%   $25.8445   $25.84   $25.85   $25.80  
  Purchase #2 $192.77   8.241%   $208.6562   $208.66   $208.65   $208.70  
  Purchase #3 $83.74   5.346%   $88.2167   $88.22   $88.20   $88.20  
  Purchase #4 $163.45   9.474%   $178.9353   $178.94   $178.95   $178.90  
  Purchase #5 $223.38   5.268%   $235.1477   $235.15   $235.15   $235.10  
  Purchase #6 $120.27   9.717%   $131.9566   $131.96   $131.95   $132.00  
  Purchase #7 $67.55   9.815%   $74.18   $74.18   $74.20   $74.20  
  7 purchase totals = $875.59       $942.9370   $942.95   $942.95   $942.90