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 $32.66   6.108%   $34.6549   $34.65   $34.65   $34.70  
  Purchase #2 $138.35   7.673%   $148.9656   $148.97   $148.95   $149.00  
  Purchase #3 $111.56   13.798%   $126.953   $126.95   $126.95   $127.00  
  Purchase #4 $130.41   6.559%   $138.9636   $138.96   $138.95   $139.00  
  Purchase #5 $235.59   12.278%   $264.5157   $264.52   $264.50   $264.50  
  Purchase #6 $167.79   12.575%   $188.8896   $188.89   $188.90   $188.90  
  Purchase #7 $105.43   6.221%   $111.9888   $111.99   $112.00   $112.00  
  7 purchase totals = $921.79       $1,014.9312   $1,014.93   $1,014.90   $1,015.10