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 $82.49   7.360%   $88.5613   $88.56   $88.55   $88.60  
  Purchase #2 $222.79   8.212%   $241.0855   $241.09   $241.10   $241.10  
  Purchase #3 $78.31   5.264%   $82.4322   $82.43   $82.45   $82.40  
  Purchase #4 $187.48   8.297%   $203.0352   $203.04   $203.05   $203.00  
  Purchase #5 $227.88   9.409%   $249.3212   $249.32   $249.30   $249.30  
  Purchase #6 $156.35   13.217%   $177.0148   $177.01   $177.00   $177.00  
  Purchase #7 $173.52   3.822%   $180.1519   $180.15   $180.15   $180.20  
  7 purchase totals = $1,128.82       $1,221.6021   $1,221.60   $1,221.60   $1,221.60