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 $36.87   11.150%   $40.981   $40.98   $41.00   $41.00  
  Purchase #2 $159.86   3.682%   $165.746   $165.75   $165.75   $165.70  
  Purchase #3 $170.77   12.531%   $192.1692   $192.17   $192.15   $192.20  
  Purchase #4 $228.91   11.540%   $255.3262   $255.33   $255.35   $255.30  
  Purchase #5 $170.80   6.135%   $181.2786   $181.28   $181.30   $181.30  
  Purchase #6 $35.72   11.192%   $39.7178   $39.72   $39.70   $39.70  
  Purchase #7 $135.53   9.227%   $148.0354   $148.04   $148.05   $148.00  
  7 purchase totals = $938.46       $1,023.2542   $1,023.27   $1,023.30   $1,023.20