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 $218.87   12.312%   $245.8173   $245.82   $245.80   $245.80  
  Purchase #2 $67.48   11.864%   $75.4858   $75.49   $75.50   $75.50  
  Purchase #3 $107.67   8.213%   $116.5129   $116.51   $116.50   $116.50  
  Purchase #4 $52.95   6.744%   $56.5209   $56.52   $56.50   $56.50  
  Purchase #5 $80.40   9.273%   $87.8555   $87.86   $87.85   $87.90  
  Purchase #6 $196.51   3.379%   $203.1501   $203.15   $203.15   $203.20  
  Purchase #7 $227.69   5.734%   $240.7457   $240.75   $240.75   $240.70  
  7 purchase totals = $951.57       $1,026.0882   $1,026.10   $1,026.05   $1,026.10