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 $53.52   13.364%   $60.6724   $60.67   $60.65   $60.70  
  Purchase #2 $154.72   6.424%   $164.6592   $164.66   $164.65   $164.70  
  Purchase #3 $37.55   9.273%   $41.032   $41.03   $41.05   $41.00  
  Purchase #4 $113.60   4.579%   $118.8017   $118.80   $118.80   $118.80  
  Purchase #5 $221.29   8.549%   $240.2081   $240.21   $240.20   $240.20  
  Purchase #6 $238.93   10.163%   $263.2125   $263.21   $263.20   $263.20  
  Purchase #7 $194.77   4.333%   $203.2094   $203.21   $203.20   $203.20  
  7 purchase totals = $1,014.38       $1,091.7953   $1,091.79   $1,091.75   $1,091.80