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 $184.49   5.255%   $194.1849   $194.18   $194.20   $194.20  
  Purchase #2 $138.72   13.352%   $157.2419   $157.24   $157.25   $157.20  
  Purchase #3 $36.73   13.432%   $41.6636   $41.66   $41.65   $41.70  
  Purchase #4 $132.92   11.558%   $148.2829   $148.28   $148.30   $148.30  
  Purchase #5 $118.31   13.780%   $134.6131   $134.61   $134.60   $134.60  
  Purchase #6 $82.61   8.227%   $89.4063   $89.41   $89.40   $89.40  
  Purchase #7 $76.90   4.705%   $80.5181   $80.52   $80.50   $80.50  
  7 purchase totals = $770.68       $845.9108   $845.90   $845.90   $845.90