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 $50.38   12.372%   $56.613   $56.61   $56.60   $56.60  
  Purchase #2 $172.94   4.691%   $181.0526   $181.05   $181.05   $181.10  
  Purchase #3 $212.65   4.403%   $222.013   $222.01   $222.00   $222.00  
  Purchase #4 $55.56   3.816%   $57.6802   $57.68   $57.70   $57.70  
  Purchase #5 $109.64   12.145%   $122.9558   $122.96   $122.95   $123.00  
  Purchase #6 $139.69   12.646%   $157.3552   $157.36   $157.35   $157.40  
  Purchase #7 $199.93   8.760%   $217.4439   $217.44   $217.45   $217.40  
  7 purchase totals = $940.79       $1,015.1137   $1,015.11   $1,015.10   $1,015.20