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 $84.96   12.475%   $95.5588   $95.56   $95.55   $95.60  
  Purchase #2 $201.42   8.710%   $218.9637   $218.96   $218.95   $219.00  
  Purchase #3 $108.73   8.237%   $117.6861   $117.69   $117.70   $117.70  
  Purchase #4 $204.94   3.779%   $212.6847   $212.68   $212.70   $212.70  
  Purchase #5 $198.52   6.499%   $211.4218   $211.42   $211.40   $211.40  
  Purchase #6 $115.45   4.232%   $120.3358   $120.34   $120.35   $120.30  
  Purchase #7 $26.87   8.194%   $29.0717   $29.07   $29.05   $29.10  
  7 purchase totals = $940.89       $1,005.7226   $1,005.72   $1,005.70   $1,005.80