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 $206.52   10.207%   $227.5995   $227.60   $227.60   $227.60  
  Purchase #2 $70.85   13.848%   $80.6613   $80.66   $80.65   $80.70  
  Purchase #3 $13.52   5.459%   $14.2581   $14.26   $14.25   $14.30  
  Purchase #4 $147.92   11.534%   $164.9811   $164.98   $165.00   $165.00  
  Purchase #5 $39.68   13.332%   $44.9701   $44.97   $44.95   $45.00  
  Purchase #6 $164.48   4.254%   $171.477   $171.48   $171.50   $171.50  
  Purchase #7 $235.79   6.566%   $251.272   $251.27   $251.25   $251.30  
  7 purchase totals = $878.76       $955.2191   $955.22   $955.20   $955.40