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 $81.31   7.263%   $87.2155   $87.22   $87.20   $87.20  
  Purchase #2 $206.85   4.762%   $216.7002   $216.70   $216.70   $216.70  
  Purchase #3 $57.52   3.671%   $59.6316   $59.63   $59.65   $59.60  
  Purchase #4 $168.28   3.436%   $174.0621   $174.06   $174.05   $174.10  
  Purchase #5 $219.68   9.749%   $241.0966   $241.10   $241.10   $241.10  
  Purchase #6 $58.33   12.703%   $65.7397   $65.74   $65.75   $65.70  
  Purchase #7 $72.93   7.243%   $78.2123   $78.21   $78.20   $78.20  
  7 purchase totals = $864.90       $922.6580   $922.66   $922.65   $922.60