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 $247.84   8.173%   $268.096   $268.10   $268.10   $268.10  
  Purchase #2 $182.88   10.666%   $202.386   $202.39   $202.40   $202.40  
  Purchase #3 $138.78   5.621%   $146.5808   $146.58   $146.60   $146.60  
  Purchase #4 $117.28   8.242%   $126.9462   $126.95   $126.95   $126.90  
  Purchase #5 $176.88   10.128%   $194.7944   $194.79   $194.80   $194.80  
  Purchase #6 $181.85   10.639%   $201.197   $201.20   $201.20   $201.20  
  Purchase #7 $58.58   8.440%   $63.5242   $63.52   $63.50   $63.50  
  7 purchase totals = $1,104.09       $1,203.5246   $1,203.53   $1,203.55   $1,203.50