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 $60.98   13.736%   $69.3562   $69.36   $69.35   $69.40  
  Purchase #2 $165.89   9.154%   $181.0756   $181.08   $181.10   $181.10  
  Purchase #3 $8.57   4.717%   $8.9742   $8.97   $8.95   $9.00  
  Purchase #4 $192.64   9.435%   $210.8156   $210.82   $210.80   $210.80  
  Purchase #5 $239.56   9.506%   $262.3326   $262.33   $262.35   $262.30  
  Purchase #6 $224.45   3.537%   $232.3888   $232.39   $232.40   $232.40  
  Purchase #7 $64.72   4.818%   $67.8382   $67.84   $67.85   $67.80  
  7 purchase totals = $956.81       $1,032.7812   $1,032.79   $1,032.80   $1,032.80