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 $133.39   9.271%   $145.7566   $145.76   $145.75   $145.80  
  Purchase #2 $24.57   6.152%   $26.0815   $26.08   $26.10   $26.10  
  Purchase #3 $219.96   10.870%   $243.8697   $243.87   $243.85   $243.90  
  Purchase #4 $174.77   11.862%   $195.5012   $195.50   $195.50   $195.50  
  Purchase #5 $147.40   5.471%   $155.4643   $155.46   $155.45   $155.50  
  Purchase #6 $139.88   13.810%   $159.1974   $159.20   $159.20   $159.20  
  Purchase #7 $124.28   12.801%   $140.1891   $140.19   $140.20   $140.20  
  7 purchase totals = $964.25       $1,066.0598   $1,066.06   $1,066.05   $1,066.20