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 $218.56   13.433%   $247.9192   $247.92   $247.90   $247.90  
  Purchase #2 $117.61   10.104%   $129.4933   $129.49   $129.50   $129.50  
  Purchase #3 $238.41   10.331%   $263.0401   $263.04   $263.05   $263.00  
  Purchase #4 $93.33   3.568%   $96.66   $96.66   $96.65   $96.70  
  Purchase #5 $235.55   13.766%   $267.9758   $267.98   $268.00   $268.00  
  Purchase #6 $139.81   5.842%   $147.9777   $147.98   $148.00   $148.00  
  Purchase #7 $165.59   9.654%   $181.5761   $181.58   $181.60   $181.60  
  7 purchase totals = $1,208.86       $1,334.6422   $1,334.65   $1,334.70   $1,334.70