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 $152.73   9.544%   $167.3066   $167.31   $167.30   $167.30  
  Purchase #2 $241.51   12.270%   $271.1433   $271.14   $271.15   $271.10  
  Purchase #3 $59.85   9.665%   $65.6345   $65.63   $65.65   $65.60  
  Purchase #4 $187.28   13.566%   $212.6864   $212.69   $212.70   $212.70  
  Purchase #5 $165.55   9.753%   $181.6961   $181.70   $181.70   $181.70  
  Purchase #6 $227.76   12.224%   $255.6014   $255.60   $255.60   $255.60  
  Purchase #7 $73.51   5.580%   $77.6119   $77.61   $77.60   $77.60  
  7 purchase totals = $1,108.19       $1,231.6802   $1,231.68   $1,231.70   $1,231.60