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 $148.43   3.250%   $153.254   $153.25   $153.25   $153.30  
  Purchase #2 $249.42   13.691%   $283.5681   $283.57   $283.55   $283.60  
  Purchase #3 $167.62   3.829%   $174.0382   $174.04   $174.05   $174.00  
  Purchase #4 $79.27   6.118%   $84.1197   $84.12   $84.10   $84.10  
  Purchase #5 $124.67   4.522%   $130.3076   $130.31   $130.30   $130.30  
  Purchase #6 $160.74   12.824%   $181.3533   $181.35   $181.35   $181.40  
  Purchase #7 $241.52   9.607%   $264.7228   $264.72   $264.70   $264.70  
  7 purchase totals = $1,171.67       $1,271.3637   $1,271.36   $1,271.30   $1,271.40