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 $33.91   10.402%   $37.4373   $37.44   $37.45   $37.40  
  Purchase #2 $228.41   12.809%   $257.667   $257.67   $257.65   $257.70  
  Purchase #3 $79.84   6.573%   $85.0879   $85.09   $85.10   $85.10  
  Purchase #4 $88.93   9.836%   $97.6772   $97.68   $97.70   $97.70  
  Purchase #5 $184.26   7.796%   $198.6249   $198.62   $198.60   $198.60  
  Purchase #6 $50.61   7.689%   $54.5014   $54.50   $54.50   $54.50  
  Purchase #7 $137.40   5.494%   $144.9488   $144.95   $144.95   $144.90  
  7 purchase totals = $803.36       $875.9445   $875.95   $875.95   $875.90