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 $186.49   10.207%   $205.525   $205.53   $205.55   $205.50  
  Purchase #2 $148.74   4.228%   $155.0287   $155.03   $155.05   $155.00  
  Purchase #3 $82.70   6.342%   $87.9448   $87.94   $87.95   $87.90  
  Purchase #4 $209.97   5.764%   $222.0727   $222.07   $222.05   $222.10  
  Purchase #5 $153.47   9.192%   $167.577   $167.58   $167.60   $167.60  
  Purchase #6 $164.52   10.236%   $181.3603   $181.36   $181.35   $181.40  
  Purchase #7 $42.91   8.650%   $46.6217   $46.62   $46.60   $46.60  
  7 purchase totals = $988.80       $1,066.1302   $1,066.13   $1,066.15   $1,066.10